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漂浮的锡纸

所属:听力板块 来源:普特英语听力 阅读:2692 次 评论:0 条 [我要评论]  [+我要收藏]

小编摘要:锡纸为一种涂上或贴以像银的膜状金属纸,多为银白色,实际上是铝箔。铝箔纸(Aluminium foil),亦作铝箔,在香港称之为锡纸,主要用于厨房煮食、盛载食物,或用来制作一些可以简单清洁的物料。

 Floating Tin Foil



How does tinfoil float? Find out on this Moment of Science.

Here’s an experiment you can do at home with your kids.

Take a sheet of tin foil and shape it into a little canoe. Now fill up the sink(水槽) with water. Now go find a young person. Ask her or him if this much tinfoil will float. Have the young person feel how heavy the tin foil is. After you’ve made your guesses, place the canoe in the water.

Yep, it floats. You say: I guess we can conclude that tin foil that weighs this much is still light enough to float, huh?

If said young person falls for this, say: Then how come when I crumple up(揉皱)the canoe into a ball, the tin foil sinks? Crumple the canoe. Down it goes. The crumpled ball weighs exactly as much as the canoe did. Why doesn’t it float?

The answer is in displacement(位移). An object that displaces(转移) its own weight in water will float, regardless of how heavy it is. That’s why multi-ton battleships(战列舰) don’t sink: as long as they push aside their own weight in water, they’ll stay on top.

Now, the canoe you made has an excellent shape for displacing water. It acts like a wedge(楔), pushing water aside as you lower it into the sink and replacing the water with low-density(低密度的) air. The crumpled ball, on the other hand, has just the wrong shape. All of its mass is compressed(压紧,压缩) together, so it has a high density throughout and displaces very little water. And down it goes!

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2012-05-07 14:35 编辑:pliny
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